Catalytic reactor



Aug 15, 1.950 c. C. wA'TsN 2,518,583

CATALYTIC REACTOR Filed June 27, 1945 Z l e f/ Patented Aug. 15, 1950 i2,518,583 CATALYTIC REACTOR Charles C. Watson, Evanston, Ill., assignorto Universal Oil Products Company, Chicago, Ill., a

corporation of Delaware Application June 27, 1945, Serial No. 601,756

This invention relates to an improved Vform of ycatalytic reactor,particularly of the elongated or tubular type. This type ofreactorernploys a fixed bed of catalytic contact material for directingor promoting a desired reaction and y'for eiecting intimacy of contactbetween reactants and this catalytic contact material.

One object of this invention is to provide an improved methodforregenerating or reactivating catalysts beds in the tubular type ofreactor.

Another object of this invention is to provide an improved tubularreactor having a reactivating gas distributing means which gives aspecifically proportioned flow of oxidizing gas to the catalyst bedduring the reactivating cycle.

A further object of the invention is to provide an auxiliary inert gasstream to control the -nate of movement ormass velocity of thedistributed reactivating gas stream within the catalyst bed and toeffect an improved transfer of theheat of combustion, which is generatedduring the re# activating process, tothe tube walls; and to limit thetemperature rise of the catalyst through the heat capacity of thisauxiliary gas stream.

A still further object of the invention is to provide an annular channelaround the catalyst containing reaction tube for the ow of a fluidstream in heat exchange relationship with the reaction tube.

Tubular type reactors having long narrow fixed beds of catalysts arepreferable in certain hydrocarbon conversion processes such as, forexample, the dehydroge'rration of butane to'butylene, or butylene tobutadiene. kThe processing or conversion reaction of the catalytic 'de'-hydrogenation process is endothermic, requiring heat transfer to arelatively high mass velocity stream of the hydrocarbon change,therefore long narrow catalystlbeds intubular type of reactors areparticularly suitable r.tor this service.

In most hydrocarbon conversion processes where a fixed bed of catalystis used,'there will Fbe a carbon deposition on the catalyst particlesduring 'the processingV period lwhich actsto-reduce the catalystactivity. This carbon deposit may be burned oi by'circulating an oxygencontaining gas over the catalyst, therefore any fixedv bed of catalystin a reactor is alternatelyV employed in processing and then subjectedto a reactivating or regeneratingoperation." In acom-v mercial plant inorder to have `continuous pro'- cessing, a plurality'of reactors areusually einployed in a tube bank and at least two tube banks used inthevplant. By means ofsuitable switch 2 lClaims. y ('Cl. 23-288) valves, onereactor tube bank is kept in processing service while the other is beingreactivated by having the carbon burned off. At specified intervals, thereactors may be automatically switched by ka time-cycle controller.

For example, during the processing operation of a dehydrogenation unit',normal butane is pumped into a heat exchanger and heater where it israised to approximately 1050 F. and then is directed by means of switchvalves to a processing reactor tube bank. As the butane enters lthereactor tubes the reaction begins to take place .and it is necessary latthis point to add heat ir the reaction is to be carried forward at thedesired rate. This heat is added by circulating hot ilue gas around theoutside of the ,catalyst tubes.

A-fter the ue gas leaves the reactor, it is conducted through ducts backto a fan, which discharges it through a heater and back into thereactor. The flue gas is directed to the proper reactor by means ofautomatic switching means located in the inlet to each reactor, and itstemperature is controlled by automatic regulation of fuel gas flow tothe heater. The material leaving the catalyst tubes is composed ofunreacted butane, butylene, hydrogen and a small percentage of otherlight gases.

In the reactivating operation, a reactivating gas of controlled oxygencontent and or suiicient volume is furnished to permit burning off ofcarbon deposited on the catalyst, without reaching excessively hightemperatures. The use of straight air for reactivation results intemperatures far in excess of 1300 F., which would substantially reducethe activity of the usual dehydrogenation catalyst within a. relativelyshort time. By the control of' the oxygen content of the reactivatingglas to between 1 and 3%, it is possible to burny 01T all the carbonwithin the allotted time without exceeding`1300 F., or the maximumallowable temperature rfor the catalyst. The burning of the'c'arboninside the catalyst tube produces heatV which must be dissipated. Partof this heat is absorbed by raising the temperature of the reactivatinggas" itself from 800 F. to approximately 1200* F., the remainderv isabsorbed by a ue gas cooling vstream which is passed around the outsideof the catalyst tubes. This coolinlg medium Amay be directed by suit`ableA switchingl means to the reactivating tube alyst tubular reactor.The distributing tube has a plurality of openings which are positionedand so proportioned from one end to the other, that a uniformly hightemperature is achieved throughout the entire length of the catalyst bedduring the reactivating cycle. A greater number of openings, or largeropenings, are placed at the inlet end of the reactor tube such that therate of oxygen supply and rate of colmbustionin the catalyst bed will begradually diminished from the inlet end to the outlet end of the bed.

In order to control and aid the transfer of heat generated from theexothermic reactivating process, to the tube walls, an auxiliary inertgas stream is provided to ow longitudinally through the catalyst bedduringr the reactivating cycle.

This inert gas stream follorws the same flowpath l as the reactant glasstream and therefore may be charged to the reactor through the sameinlet as that used by the reactants. The change in the charge streamsfrom processing to reactivating may be accomplished by proper placing ofvalves or the use of suitable switch valves. This relatively inert gasstream, containing little or no oxygen, flows in conjunction with. thedistributed oxidizing gas stream for the duration of the reactivationperiod and in addition is provided at a relatively high mass velocity sothat the best [possible transfer of the heat of vcombustion to the outertube Wall may be obtained.

By effecting a relatively uniform reactivation temperature in thecatalyst bed it is possible to approach the given maximum allowablecatalyst temperature and thereby attain a maximum carbon burning anduniform carbon removal from y the particles in the bed.

A tubular sleeve placed around and spaced away from the catalystcontaining reaction tube is also provided with Vthis improved tubularren actor to form an annular, confined channel for L,

the heating or cooling medium to ilow in controlled heat exchangerelationship with the reaction tube. For the processing period withinthe catalyst bed a hot fluid medium may be passed through the annularflow channel to furnish heat for an endothermic reaction, and a-less hotcooling medium may be passed therethrough during the exothermicreactivation period. It is further known that there is an optimum sizesleeve which provides the most advantageous heat exchange relationship.

There are at present various forms of reactor tubes which have .beendevised and are in use. Distribution improvements have also been made tothe elongated or tubular type of reactors; however, such improvementshave primarily been for the purposeV of decreasing the pressure drop Vofthe fluids flowing therethrough. In general, present types'of tubularreactors are constructed so that the reactivating gas stream must followthe same flow path that the processing gas stream travels during theconversion cycle. However, with long narrow xed catalyst beds such ascontained in reactors of the tubular type wherein alternatingendothermic and exothermicl processes occur, it is more desirable andeiicient Yto provide different flow paths, such as provided by thisinvention. In this invention the perforated reactivating gasdistributing tube which extends longitudinally into the catalyst bed isprovided not so much for pressure drop reduction, but for the purpose ofacquiring uniform oxidation and a uniform high temperature throughoutthe bed. During the reactivation process of present solidly packedtubes, containing catalyst such as is used in the dehydrogenation ofhydrocarbons, combustion proceeds in a relatively narrow zone, when allthe oxygen is introduced at the inlet to the bed. Thus, high localcatalyst temperatures are reached in this zone, the remainder of thetube being relatively ineffective for removing the heat of combustion.

Briefly, this invention embodies means for im proving the reactivationof a catalyst bed in a tubular type reactor, the means compriseproviding a centrally positioned distributing tube having perforationswhich decrease in number throughout the length of the catalyst bed, aninert gas stream passing at a relatively high velocity through theelongated catalyst bed, and an enclosing sleeve around the catalystretaining reaction tube to accommodate a heat exchange fluid streamwhich is passed externally around the reactor tube to flow concurrentlywith the internal inert gas stream and longitudinally with the catalystbed.

The accompanying drawing and description thereof should make moreapparent the features comprising the improved reactor tube andreactivation method.

Figure 1 shows one form of tubular reactor provided by the invention ina sectional eleva# tional view.

Figure 2 shows a sectional plan view through the reactor tube asindicated by line 2-2 in Figure l.

Referring to the drawing, the tube l contains a bed 2 of catalyticmaterial and forms an elongated reaction tube. A plurality of thesetubes or tubular assemblies in a tube bank, are normally used in acommercial plant, each of the tubes in a given bank being connected tocommon header conduits and operating simultane ously. The tube l isprovided Ywith flanges 3 and 4 at the top and bottom ends, respectively.The upper flange 3 on the tube'l has a companion flange or cover 5 whichforms an end closure to the chamber, at the same time it is xedlyattached to a gas vinlet and distribution tube `i5,

which extends therethrough and which is perforated by aplurality ofsmall holes or slots. The tube 5 extends into and substantially all theway through the catalyst bed 2. Thel perforated holes in the tube E aspreviously noted are not necessarily equally spaced throughout theembedded length. Since this distribution tube functionsV to effect asubstantially uniform reactivation temprature in the catalyst bed it isdesirable to vary or proportion the hole spacing, having a greaternumber of holes near the upper part vof the bed. Thus, the rate ofoxidation will be somewhat less at the lower end of the bed. However,the catalyst bed temperature will be increased in the lower portiony bythe downward movement of hot gases from above so that the net effect isa relatively uniform temperature throughout the elongated bed.

The lower flange 4 has a companion flange or cover 1 which forms abottom closure member. An outlet conduit tube 8 is connected to thislower cover member l, and may be used to alternately remove conversionproducts and reactivation combustion products from the catalyst bed 2and reaction tube I.

vThe companion flanges 5 and 1 may be attached by suitable bolts, notillustrated, to their respective tube vflanges 3 and 4, also, suitablegaskets 9 are provided between each of the companion flanges. Aperforated plate or screen-like member l0 is provided just above thebottom cover 'I andover the outlet conduit 8. This plate I0 serves tosupport and retain the catalytic material within the tube I, preventingit from carrying into the outlet pipev. When it is desired to remove thebed of catalytic material, itfcan be removed or dumped by detaching thecover 'I and allowing theperforated plateA I to fall out. The removableupper cover plate is particularly advantageous from the standpoint ofproviding ready means to place catalyst into the tube I, or to rei-lllthe reactor tube I with catalytic material when it has been dumped.Reactant or reactivation fluids or other materials may be charged to thereactor tube by way of the upper side inlet conduit II.

As previously noted, in a commercial plant, reactor tube assemblies suchas in the Figure 1, are normally used in plurality, at least one bank oftubes in a common cell are processing simultaneously while another tubebankjin a different cell has tubes being simultaneously reactivated.Thus, in any reactor tube bank, each of the tubes 6, 8, and I I willconnect to headers which in turn are connective with each reaction tubeassembly in the reactor bank.

In the drawing, the plate I2 indicates a tube sheet or support plate atthe upper end of a cell containing a plurality of tubes I. The plate I2is provided with an insulating material I3 which is suitable for thetemperature to be encountered. The plate I4 provides a baille within thecell, in order that the heating or cooling gases which are employed willbe channeled through the annular space between tube I and sleeve I5. Ina tube bank where there is a plurality of tubes, a more equaldistribution of gases, a greater uniformity in tube temperatures, and animproved heat transfer rate is accomplished by the use of sleeves I5around each of the reactor tube assemblies. The sleeve I5 may be fixedlyattached to the tube I by spaced lugs or web plates I6 at the uppersupported end of the tube I, while spacer bars I'I attached to the lowerend of tube I will serve to keep the sleeve I5 in proper alignment andat the same time permit diierential expansion to take place between thetwo tubes.

A lower tube sheet I8 having insulation I9 is provided near the lowerend of the tube I to form the bottom of the enclosing cell or chamber.The general arrangement shown, with the baffle plate I4 near the top,and the directional arrows, indicate the flow path of the heating (orcooling) gases to be in at the top of the sleeve I 5 and out at thelower end, such that concurrent flow is obtained with the processing orreactivating gases which also are charged to the tube I at the upperend. Of course, it may be desirable for certain processing orreactivating operations to have the heating or cooling gas flow upwardto eiect countercurrent heat exchange relationship with the internalflow.

Figure 2 of the drawing shows a conventional section through the tubularreactor as indicated by the line 2-2 of Figure 1. The various parts arenumbered to correspond to the reference numerals attached in theelevational view, Figure 1.

To illustrate the operation of the improved type reactor tube, let it beassumed that it is to be employed in a process of catalytic butanedehydrogenation, which means the removal of hydrogen from butane in thepresence of a suitable catalyst to form butylene and hydrogen. Thereaction is carried out in the tube I at temperatures ranging fromapproximately 1000 F.

to 1100o F. and pressures ranging from approximately ten to fty poundsper square inch.

During the dehydrogenation processing period, normal butane which hasbeen heated to reaction temperature of approximately 1050 F. is chargedto the top of the tube I by way of inlet conduit I I. As the butaneenters the catalyst bed 2, the reaction begins to take place; and inorder for the reaction to be carried forward at the desired rate, heatmust be added. Heat is furnished by hot flue gases which are passed tothe reactor cell and circulated through the space provided between tubeI and sleeve I5. The hot external flue gas is brought to the annularflow channel within sleeve I5 at approximately 1450 F., it gives up heatto the endothermic reaction inside the reaction tube I and leaves thelower end of sleeve I5 at a temperature of approximately 1250" F. Thebutane passes downward through the annular shaped catalyst bed 2 and thereaction products or material, leaving the tube by way of outlet conduit8, is composed of unreacted butane, butylene, hydrogen and a smallamount of other light gases. In this processing operation a carbondeposit is left on the catalyst particles, such that its activity isreduced and regeneration is then required.

During the reactivating period, the carbon deposit is removed from thecatalyst by a burning-off or oxidizing process. As previously noted,

. this reactivating operation must be closely controlled to preventoverheating the catalyst and at the same time effect a high temperaturefor an emcient reactivation. The ideal condition is to obtain anapproximately constant or uniform temperature throughout the length ofthe catalyst bed, without effecting a detrimental temperature buildup atsome point in the bed. In the improved apparatus and method ofreactivation of this invention the reactivating gas containing acontrolled small percentage of oxygen is charged by way of conduit 5 tothe catalyst bed. This conduit 5 having perforations so proportioned inits embedded length that a uniform temperature is obtainable, makes itpossible to eiect as high an allowable temperature, without impairingcatalyst activity. Cooling gas is circulated to the sleeve I5 to aid incarrying away and dissiplating the heat produced by the oxidation insidethe catalyst bed 2. A relatively inert gas, having very little if anyoxygen content, is passed by way of inlet conduit I I into the upper endof tube I and flows for the same period as the reactivating gas stream.This inert gas stream is passed at a relatively high velocity in orderto effect good transfer of heat of combustion to the tube wall I. Thecooling gas stream entering the top of sleeve I5 may be ue gas providedat a temperature of approximately 900 F. and leaving the bottom of thecell at about 1200 F.

With the rate of oxygen supply being `proper-- tioned by the newdistribution tube 5 so that there is a gradual decrease from' top tobottom of the bed, there is therefore, a corresponding gradual decreasein the rate of combustion. The rate of h-eat transfer from the tube tothe cooling gas similarly decreases, although of course it should benoted, the temperature of the cooling gas itself gradually increasesfrom top to bottom in sleeve I5 due to absorbed heat. The ltotal effect,or resulting operation is that a more constant or relatively uniformlyheated catalyst bed is obtained. Switching valves or means not shown,will of course be required on each of the inlet and outlet conduits sothat proper change-over can be easily made from vthe processing to thereactivating cycle and vice versa.

Although the operation of this reactor tube has been described inconnection with the dehydrogenation process, it is not intended to limitthe improvement in the tubular reactor to this use only. Other Xed bedcatalytic conversion processes may well make Yuse of a similar reactor.Also, it is not intended to limit the invention to the -exact form ofapparatus as shown, as obviously many variations irl-constructiondetails and form may be made and still come within the scope of theinvention.

I claim as my invention:

1. A reactor comprising a tubular housing having a reactant inlet at oneend thereof and a product gas outlet at its opposite end, alongitudinally perforated regenerative gas conduit within and spacedfrom the Wall of said housing and substantially coextensive in lengthwith the housing, the total area of the perforations per unit length ofthe regenerative gas conduit gradually and successively decreasing fromthe reactant inlet to the product gas outlet, means for retaining asolid contact material in the space between said conduit and housing',an open-ended tubular sleeve spaced from and surrounding a substantialportion of said housing, and means for passing a heat exchange mediumthrough the space between said sleeve and housing.

2. The reactor of claim 1 further characterized in that the number ofperforations per unit length of said conduit decreases from said inletto said outlet.

CHARLES C. WATSON.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,782,435 Merriam Nov. 25, 19301,828,146 Joseph Oct. 20, 1931 1,989,927 Houdry Feb. 5, 1935 2,042,469Joseph June 2,1936 2,073,638 Houdry Mar. 16, 1937 2,162,893 Kuhl June20, 1939 2,278,892 Nagle et al Apr. 7, 1942 2,336,879 Mekler Dec. 14,1943

1. A REACTOR COMPRISING A TUBULAR HOUSING HAVING A REACTANT INLET AT ONEEND THEREOF AND A PRODUCT GAS OUTLET AT ITS OPPOSITE ;END, ALONGITUDINALLY PERFORATED REGENERATIVE GAS CONDUIT WITHIN AND SPACEDFROM THE WALL OF SAID HOUSING AND SUBSTANTIALLY COEXTENSIVE IN LENGTHWITH THE HOUSING, THE TOTAL AREA OF THE PERFORATIONS PER UNIT LENGTH OFTHE REGENERATIVE GAS CONDUIT GRADUALLY AND SUCCESSIVELY DECREASING FROMTHE REACTANT INLET